Due to their thermal stability, perfluoropolyether fluids have a great potential for use as engine oils, hydraulic fluids and greases. However, a drawback in their use results from the fact that certain metals are corroded by such fluids at temperatures of about 550° F. and above in an oxidative environment.
In U.S. Pat. No. 4,454,349, the preparation of perfluoroalkylether-substituted phenyl phosphines, having the structure of Formula 1 below, is described:
wherein
Rf—O—Rf is a perfluoroalkyl ether group containing at least one ether linkage. Examples of Rf—O—Rf included:
C3F7O[CF(CF3)CF2O]xCF(CF3)—,
C2F5O(CF2CF2O)yCF2—, and
CF3O(CF2O)zCF2—,
wherein
x, y, and z are zero or an integer having a value of 1 to 20 and preferably 1 to 4.
Such phosphine derivatives are disclosed as being corrosion and oxidation inhibitors in polyfluoroalkylether polymeric fluids in long-term and wide temperature range applications. Temperature ranges are typically −100° F. to greater than 550° F., (−73° C. to greater than 288° C.). Incorporation of these compounds in perfluoroalkylether fluids inhibits the oxidation-corrosion of various metals with which the fluids come into contact. These additives also prevent decomposition of such fluids when exposed to a high-temperature oxidative environment.
The effectiveness of perfluoropolyether-substituted phosphines as oxidation inhibitors in perfluoropolyether fluids is well known to those skilled in the art and has been described and quantified in several patents, for instance by Snyder, et al., in U.S. Pat. Nos. 4,438,006 and 4,438,007, and by Christian, et al., in U.S. Pat. Nos. 4,431,555, and 4,431,556. Perfluoroalkyl substituted phosphines have been used in fluorous phase catalyst systems, Hope, et al., Polyhedron 18(22), 1999, pp. 2913-2917.
However, the synthesis described in U.S. Pat. No. 4,454,349 involves multiple steps requiring the use of hazardous and pyrophoric reactants and reaction temperatures ranging between −80° C. and 200° C. The process includes two reaction steps requiring n-butyllithium and an intermediate sulfur tetrafluoride/hydrogen fluoride fluorination step. Consequently, such potentially useful perfluoroalkylether substituted phenyl phosphines have remained effectively inaccessible.
The mechanism of free-radical perfluoroalkylation of aromatics has been studied and discussed by Bravo et al., in Journal of Organic Chemistry, 62(21), 1997 pp. 7128-7136. Bravo et al. studied the reaction of a perfluoroalkyl iodide (such as perfluoro-n-butyl iodide) with various aromatic compounds, including benzene and biphenyl.
It would be desirable to improve the synthesis of the perfluoroalkyl and perfluoropolyether-substituted aryl phosphines, such as the phenyl phosphines described above, and to have available the antimony and arsenic analogs. The present invention provides such a process.